dripping acorn trees

Asked November 30, 2020, 7:26 PM EST

Every spring the acorn trees in the little Sweet Home senior community place I live drips this stuff. I believe its from aphids? What can I use on the trees that would stop this?

Linn County Oregon

4 Responses

It is possible that what you are experiencing is honeydew drip from aphids, but this is not usually a big problem on oak trees. I would need to see photos of the tree to identify it, and of the problem (especially any insects that are present) in order to diagnose this and help you. There is probably nothing you could do about it at this time of year anyway. Why don't you contact us again in the spring when the problem begins, and send photos (or bring samples to your Extension office).

I wanted to ask early so that I could maybe apply whatever might be needed before the problem as it drips so badly that our cars are covered and the ground gets sticky.

Sorry that is the totally wrong picture... Anyway. I knew it was aphids and what I wanted to know was what to use and when to use it.

Aphids are a fairly common problem on some landscape trees - lindens are especially notorious for attracting them. It is a difficult problem to address because of the size of trees. Non-toxic methods include knocking the aphids off when they start to appear with a strong spray of water - even a power washer, for a large tree. But if the tree is too large this may be impractical.
Natural enemies such as ladybugs, lacewings and the like can greatly reduce an aphid population, as do small birds that eat them. If you release natural enemies when the aphids appear and have a bird-friendly yard, they will help, though they will never completely get rid of the aphids.
Chemical methods, even relatively non-toxic horticultural oils and soaps, are also problematic because of the size of trees. Spraying of large trees is best done by professionals. Most general insecticide sprays that kill aphids also kill many other beneficial insects, and sprayed on the scale of a large tree, they can do a lot of damage.
Generally the best choice for trees is a systemic insecticide, which is applied to the soil and travels throughout the tree. But these are highly toxic to bees and other insects that may feed on the flowers when they are poisoned, so if you use them, follow the instructions VERY precisely (this is true of all insecticides, of course).
None of these treatments would be applied now. Generally the best time to start is when the very first aphids appear. If you scout regularly in early spring, and knock back the early populations, it can greatly reduce later infestations (even a water spray can do this quite effectively).

Honestly, the best solution for honeydew dripping from trees is to not park under the trees during the relatively brief time it is a problem.